Mythical dragons are not invincible, all knowing, or all powerful. While considerably stronger than humans to the point where a dragon is to human, as human is to ant, a colony of ants can easily kill a human en-mass.
Mythology in europe is replete with the theme of the brave knights slaying the killer dragon.
For instance, your typical dragon is the size of a dinosaur, more or less. This means thick, heavy bones, large, slow-twitch muscles, and a very massive energy intake requirment.
Add to that the synthesis of reactive exhalation compounds, and mythically "melts gold hot" body temperatures, and you have a creature who's metabolism is running rampant, and is literally on the edge of spontaneous combustion.
(I forget where I read it, but dragons supposedly hoarde gold because it melts when they sleep on it, and gets slushy, making it super soft and comfy. Its rarity amd materialistic value are unimportant to the dragon.)
A dragon, therefore, would spend most of its time eating, and replenishing water that it exhales to stabilize body temperatures. Wings most likely serve more as a wide surface area to expell waste hat than for actual flight. (To fly, the dragon's wings would have to be hundreds of feet across, and the bones in them would have to be stronger than our best titanium steels. Remember, these wings flap. That means flexing stresses, momentary stress yeilds, and tortional stresses not found on fixed wing flying objects, like aircraft. I work in avionics. A dragon couldn't fly, even if their entire skeleton was made of pure titanium and carbon nanowire.)
You can clearly see where I am going with this. Dragons are bad asses, but their very strengths introduce weaknesses. Getting a dragon to ingest high temperature cataysts would result in them exploding spectacularaly, for instance. Metallic sodium suspended in mineral oil would work nicely in this regard.
Also, subjecting them to sustained high temperatures, like a magmaflow, would saturate their tissues in heat, resulting in very rapid onset heat prostration, and death.
Dragons are therefor, not "sue" when thought about logically. They only become sue when "because magic!" Gets thrown in. because "because magic!" Does this for just about anything where magic is not sufficiently limited, "magic" becomes an aspect of world ending proportion very quickly, and is highly discouraged. If magic exists, then it has to exist in a fashion compatible with obervable reality, which means fundemental limitations. (Otherwise your magical armor that can withistand all impacts by using the energy used to break it to reinforce the armor can faceplant into the schwatrzchild limit, and becomes a black hole once you push enough energy on it. This is due to the infamous e=mc^2 of relativity. The energy your armor absorbed is equivilent to mass, and after a certain density threshold, breaches the shwartzchild radius, and the armor implodes. Its worse than that though, because to hold back its own implosion, it draws more magic to keep it at bay, so it ends up not just being a black hole, but one that destroys all of the reality it inhabits as an infinite flow of energy is exerted, and adds to the hole's mass potential. Basically, indestructale magic armor is a timebomb, of world ending proportions, if you make magic limitless.)
Basically, what I am getting at is that invincible "anythings" are fundementally incompatible with observed reality, even in the broken over-unity, second-law-less physics of the DF universe.
The absurd materials already present in the DF universe are already close to world ending as-is. Slade is particularly diabolical in that respect.
When it comes to writing fiction, you have to create a very delicate balance between "sufficiently larger than life as to be interesting to the reader", and "so blatantly over the top that disbelief cannot be suspended."
This is especially hard with an audience like the people on this forum, some of whom probably know what a "schwartzchild radius" already is without using wikipedia, and as such are much harder to get to believe in your fantasy sufficiently to find enjoyment.
Basically, sticking with real materials and just being clever is safer than inventing unobtanium and making it work. Magic has to be limited, or else the logical consequences are a universe that in no way resembles the one the reader is from, making it too alien to believe.
I am gonna get off the soapbox and end the meta-commentary now, but I don't have a problem with intelligent dragons that can squash people like bugs. What I have a problem with is inventing new impossible materials as a deus ex machina, and creating dragons that don't have weaknesses of any kind.
Those are unforgivable sins, which make the roleplay game not fun to play anymore.